Circuit for converting time delay to voltage

ABSTRACT

A CIRCUIT FOR CONVERTING THE TIME DELAY BETWEEN TWO SIGNALS UTILIZES THE FIRST SIGNAL TO TURN ON A MONOSTABLE MULTIVIBRATOR BISTABLE MULTIVIBRATOR. THE SECOND SIGNAL TURNS OFF THE IS INTERGRATED AND FED BACK TO THE MONOSTABLE MULTIVIBRATOR REFERENCE INPUT. THIS CHANGES THE MONOSTABLE MULTIVIBRATOR OUTPUT TOWARDS THE LEVEL OF THE BISTABLE MULTIVIBRATOR OUTPUT. WHEN EQUILIBRIUM IS REACHED THE INTEGRATOR OUTPUT IS A MEASURE OF THE TIME DIFFERENCE BETWEEN THE TWO SIGNALS.

United States Patent inventor Joseph Rysnik Monroevllle, Pa. App] No.792,935 Filed Jan. 22, 1969 Patented June 28, 1971 Assignee UnitedStates Steel Corporation CIRCUIT FOR CONVERTING TIME DELAY T0 VOLTAGE 6Claims, 2 Drawing Figs.

U.S.Cl. 324/189, 73/194,324/s3,32s/133 Int. Cl c04r9/0o Field otSearch324/68, 83,

88, 70, 78, 77 (Cursory); 328/133, 134; 307/232. 295; 73/194, (I), (E),(inquired) [56] References Cited UNITED STATES PATENTS 3,325,730 6/1967Des Brisay l 324/68 3,205,438 6/1965 Buck 328/133 PrimaryExaminerMichael J. Lynch Attorney-Rea Cv Helm 1e rnmsoucsn 2a 24 26 -22sou/vac '2 4 l sauna! I s UAR/N6 SOUAR/NG Aim IFIER 28 AMPLIFIER 1 E3234 I m VERTER |aa as //v VERTEI? I 44 4a 5/ s TABL E MONO-S7431. E MULr/ we. TOR MUL r/ V/BRA roe 4mm; VOL r405 ji t IFIER 56 49 FOLLOWER VOLT4 65 FOLLOWER $05 TIM crap 5s IMTEGRATOR PATENTED JUH28 I971 SHEET 2 BF2 IN VEN TOR. TIME JOSEPH PYS/V/K dz/(45 1 CIRCUIT FOR CONVERTING TIMEDELAY TO VOLTAGE This invention relates to a circuit for providing avoltage related to the time delay or elapsed time between two correlatedevents.

One method of determining the velocity of a fluid in a stream is tomeasure the time required for radioactive tracers or medium densityvariations to pass two spaced apart sensors at fixed locations on thestream. This time is a measure of stream velocity. The time lapse can bemeasured with a high frequency oscillator and a counter. In order toprovide a voltage related to velocity, the count is converted to avoltage and the reciprocal of the voltage obtained. This method requiresso much elaborate equipment as to be undesirable.

According to my invention, a signal from an upstream sensor turns on abistable multivibrator and a monostable multivibrator. A signal from adownstream sensor turns the bistable multivibrator off. The ON time ofthe monostable multivibrator is subtracted from the ON time of thebistable multivibrator by an adder-subtracter circuit. The difference,either negative or positive, is' integrated and the integrator outputfed back to the reference input of the monostable multivibrator. if thereference voltage increases, the subsequent ON time of the monostablemultivibrator will decrease. If the reference voltage decreases,subsequent ON time will increase. lf the input signals repeat with aconstant time separation, the difference between the bistablemultivibrator ON time and the monostable multivibrator ON time becomessmaller because of the feedback. The integrator output then reaches apoint of equilibrium which will be maintained until a subsequent changein signal separation time occurs.

it is therefore an object of my invention to provide a circuit forconverting the time between two correlated events into a voltage.

Another object is to provide such a circuit which develops a magnitudeand direction correcting voltage from a first pair of correlated eventsto apply to a succeeding pair of correlated events.

These and other objects will be more apparent after referring to thefollowing specification and attached drawing in which:

FIG. 1 is a schematic diagram of the circuit of my invention used todetermine velocity of material flowing through a conduit; and

FIG. 2 is a diagram of voltage waveforms at selected locations in thecircuit of my invention..

Referring more particularly to the drawing, reference numerals 2 and 4indicate sources of two correlated time varying electrical signals 6 and8.

Signals 6 and 8 may be any correlated waveforms such as sine, square, ortriangular-shaped waveforms, or pulse trains separ' ed by the time to bemeasure. However, my invention will be described with signals 6 and 8 asa series of negative going pulses used in fluid velocity measurement.Capacitors l and 12 detect density changes in a fluid F flowing throughconduit i4. Transducers 16 and 18 convert the density changes to voltagechanges, which, after passing through capacitors 20 and 22,respectively, become voltage waveforms 24 and 26. Voltage waveforms 24and 26 are converted to waveforms 6 and 8, respectively, when sources 2and 4 are comparators biased at a fixed voltage so that the comparatorsare essentially detecting zero crossovers of waveforms 24 and 26.Signals 6 and 3 are connected to squaring amplifiers 28 and 30,respectively, which may be a Model T-306, manufactured by the EngineeredElectronics Corporation, 1441 E. Chestnut Avenue, Santa Ana, Calif. oneof several components of my invention made by the same manufacturerwhich are hereinafter designated with the prefix Model T.

Outputs 32 and 34 of amplifier 28 and 30, respectively, are connected toinverters 36 and 38, respectively, which may each be one half of a ModelT-l 36. Output 40 of inverter 36 is connected to an ON input of abistable multivibrator 42 which may be a Model T-l03. OUtput 44 ofinverter 38 is connected to an OfF input of bistable multivibrator 42.ON output 46 of bistable multivibrator 42 is connected to a voltagefollower 48 which may be a Model 19-105-1 manufactured by theConsolidated Electrodynamics Corporation, Devar Kinetics Division, 706Bostwick Avenue, Bridgeport, Conn., one of several components of myinvention made by the same manufacturer which are hereinafter designatedwith the prefix Model 19.

Output 50 of voltage follower 48 is connected to a positive input of anadder-subtracter 52 which may be a Model 19-30 1. Output 54 ofadder-subtracter 52 is connected to an integrator 56 which may be aModel l9-407. Output 58 of integrator 56 is connected to a voltmeter 60,and also to a reference input of a monostable multivibrator 62.Multivibrator 62 may be the type described in Rudolph U.S. Pat. No.3,539,934 entitled "Monostable Multivibrator Circuit with a LinearVoltage Controlled Pulse Width" dated Nov. l0, 1970, which provides anoutput pulse width which is proportional to a reference voltage. Signal6 is also connected to a trigger input of multivibrator 62. Output 64 ofmonostable multivibrator 62 is connected to a squaring amplifier 66which may be a Model T-306. Output 68 of squaring amplifier 66 isconnected to an input of a voltage follower 70 which may be a Model19-105-1. Output 72 from voltage follower 70 is connected to a negativeinput of adder-subtracter 50.

In operation, assume that negative going pulses 6 and 8 as shown in FIG.2 are applied to amplifiers 28 and 30 from sources 2 and 4,respectively. The pulses are amplified and inverted to waveforms 40 and44 at time t indicated in FIG. 2. The positive going edge of waveform 40turns multivibrator 42 on, starting the negative going edge to waveform50. At time 1,, the positive going edge of waveform 44 turnsmultivibrator 42 off, thereby completing the negative pulse of waveform50. The pulse width of waveform 50 is therefore proportional to the timedelay between pulses of signals 6 and 8.

Signal 6 is also applied to the trigger input of monostablemultivibrator 62 turning multivibrator 62 ON, thereby producing anegative going pulse waveform 72 which has a pulse width proportional tothe voltage level of output 58 from integrator 56. Waveforms 50 and 72,when connected to adder-subtracter 52 produce a waveform 54 which is thedifference between waveforms 50 and 72. Adder-subtracter 52 producespositive going pulses when waveform 72 has a pulse width longer than thepulse width of waveform 50 and a negative going pulse when waveform 72has a pulse width smaller than the pulse width of waveform 50.

At time integrator 56 begins to provide an output voltage 58 whichincreases for the duration of the width of the pulse of waveform 54.This provides a new reference level voltage to multivibrator 62 for thenext pulses received from sources 2 and 4 which in turn provides asecond and shorter pulse in waveforms 54 from 1 to t.,. This processcontinues with each set of pulses from sources 2 and 4 tending to makethe pulse width of waveform 72 derived from multivibrator 62 equal tothe pulse width of waveform 50 derived from multivibrator 42. When thetwo pulses are the same width, the voltage output 58 will be steady andits magnitude is a measure of the time difference between the pulsesfrom sources 2 and 4.

The waveforms to the left of the broken line of FIG. 2 indicate theoperation of the circuit when the flow of fluid F may be increasing orwhere voltage 58 at least initially is small enough that the pulse widthof waveform 72 is greater than the pulse width of waveform 50. Thewaveforms to the right of the broken line in FIG. 2 indicate thewaveforms in the circuit when the flow of the fluid F may be decreasingor where the voltage 58 at least initially is large enough so that thepulse width of waveform 72 is less than the pulse width of waveform 50.Waveform 54 not only shows the magnitude of the correction to be made,but also the direction of the correction.

The squaring amplifiers, voltage followers and inverters are only usedto condition the waveforms for use by components having different inputrequirements. This circuit produces a voltage directly related to thevelocity of a fluid as measured by the fluid density changes passingbetween two stations.

While one embodiment of my invention has been shown and described, itwill be apparent that other adaptations and modifications may be made.

I claim:

l. A circuit for converting a time delay to an output voltage comprisingfirst means for providing two correlated waveforms separated by the timedelay which is to be converted to the output voltage, second meansresponsive to a pair of correlated variations in said waveforms andconnected to said first means for providing said waveforms for providinga first pulse having a width directly proportional to the time betweensaid pair of variations, third means responsive to the first occurringone of the pair of correlated variations and connected to said firstmeans for providing a second pulse, said second pulse having a widthrepresentative of a reference input voltage connected to said thirdmeans, fourth means connected to both said second and third means andresponsive to the pulses from each pair of correlated variations forproviding said output voltage whose value is representative of thedifference in pulse width between said pulses, and fifth meansconnecting said output voltage as said reference input voltage to saidthird means thereby tending to change the width of the next succeedingpulse from said third means to equal the width of the pulse from saidsecond means.

2. A circuit according to claim 1 in which the second means is abistable multivibrator and the third means is a monostablemultivibrator.

3. A circuit according to claim 2 in which said monostable multivibratorhas a pulse width proportional to said reference voltage.

4. A circuit according to claim 1 in which said fourth means includes anadder-subtractor providing a voltage output pulse having a widthrepresentative of the difierence between the pulse widths of each pairof correlated pulses from said second and third means, and sixth meansconnected to said addersubtractor for integrating successive pulses fromsaid addersubtractor. I

5. A circuit according to claim 4 in which said voltage output pulsesvary in width and polarity.

6. A circuit according to claim 4 including means to display the outputof said sixth means.

